Military service members engage in unhealthy drinking at higher rates than the general public, causing health consequences and affecting force readiness. For those returning from combat deployment to Operation Enduring Freedom (OEF) and Operation Iraqi Freedom (OIF), unhealthy drinking may be exacerbated by acute stress reactions and injury, including traumatic brain injury (TBI), which is common among service members in OEF/OIF. Although civilian research suggests that impairments due to TBI may lead to an increased risk for unhealthy drinking, scant military research exists to examine whether TBI influences drinking behaviors among service members and evidence to date has been mixed. Further, TBI and posttraumatic stress disorder (PTSD) have overlapping symptoms and may co-occur, thus complicating assessment for both conditions. The three research aims of this application are to: 1) compare the post-deployment drinking behaviors for service members who experienced a TBI to those who did not, 2) to examine the relationship between experiencing a TBI and post-deployment drinking-related negative consequences, and 3) to examine the possible mediational effect of PTSD on the relationship between having experienced a TBI and the two outcome variables (drinking behaviors and negative post-deployment consequences). To analyze these research aims, this study will use the 2008 Department of Defense Survey of Health Related Behaviors among Active Duty Military Personnel, a worldwide population-based assessment. The survey was self-administered and anonymous with a response rate of 71.6 percent. The proposed study is a quasi-experimental design. The study sample includes a cohort of service members with a recent combat deployment (past year) and at least six months post-deployment before completing the survey (over 4,000 respondents), allowing the study to examine post-deployment drinking behaviors and consequences. The study will use multivariate linear and logistic regressions to assess the relationship between experiencing a TBI and 1) drinking behaviors and 2) negative consequences, as well as path analysis to examine whether PTSD mediates the relationship between TBI and drinking behaviors and negative consequences. This study is significant because it will use a population-based assessment of the military to examine the gap in knowledge regarding the association between combat-acquired TBI and post-deployment drinking and consequences, with attention to impacts on younger service members. The study is strengthened by improving upon methods for measuring combat-related TBI and addressing the controversy in the field about potential confounding between TBI and PTSD by using path analysis techniques. This innovative research application will inform future research, thus providing the Department of Defense (DOD) with information to design targeted early and secondary intervention practices to address unhealthy drinking and its consequences, helping to reduce the negative impacts to military personnel and the DOD.